The money was "created out of thin air" is the loaning bank's debt to the account the borrowed money is assigned to, not the bank's asset, so there's a very real cost to them if the borrower defaults and stops repaying them. Banks can become bankrupt, just like any other business, and no, they can't "print" their way out of it.
If you're still struggling to believe there's no real cost of defaults to banks, I invite you to look up bank insolvencies. Perhaps someone could make a wtfhappenedin2007 website.
I'm also chuckling away at you complaining that the current system means mortgages take too long to pay off a sentence after complaining that people who get into debt are rewarded! For the record, what you're actually advocating for with higher "free-market" interest rates is that poor people pay rich people more over the course of 25 years than they currently do over 35 or even 50 years to secure a house, which is less likely to appreciate in value. US home ownership rates were down at 40% before governments got involved in the mortgage market. It's impossible to pretend that anyone benefits from such a system other than people who are much, much richer than average home buyers.